1. Field of the Invention
This invention relates to a marking apparatus for coloring a lateral edge of a continuous sheet, for example, of paper moving in a direction of the length thereof.
2. Prior Art
Generally, a sheet of paper is continuously produced by a paper machine, and a continuous length of plastics film is produced by extrusion. Such sheet and film (hereinafter referred to as "sheet") are relatively wide and therefore need to be cut widthwise to a suitable size. An apparatus for cutting a sheet is commonly known in the trade as a winder which advances a sheet longitudinally and cuts it widthwise into a plurality of narrower sheets, the sheets thus cut being rolled up a predetermined length. Another cutting apparatus is known in the trade as a sheet cutter which advances a sheet longitudinally, cuts the sheet widthwise into a plurality of narrower sheets, and then cuts each segments longitudinally into rectangular sheets which are stacked one upon another.
The sheet processed by the above winder and sheet cutter may have defects such as a hole and irregularities on a sheet surface, and it has been proposed to detect such defects and apply a marking to a lateral edge of the sheet at a position disposed in registry with the defect on the sheet so that even after the sheet is either rolled up or stacked, the defect can be easily located visually from the outside thereof. The marking indicative of the detect is applied to the lateral edge of the sheet because such a smeared edge hardly affects the quality of the final sheet. Japanese Patent Application Laid-Open (Kokai) No. 58-114899 filed Dec. 26, 1981 discloses a marking apparatus for coloring the lateral edge of the sheet with a coloring element of a solid material resembling a crayon. This marking apparatus is advantageous over a marking apparatus employing ink or liquid coloring material because it does not suffer from the problem of ink leakage. However, it is rather difficult to bring the coloring element into proper contact with the lateral edge of the sheet. More specifically, the conventional marking apparatus comprises a roller, and a coloring element of a solid material mounted coaxially within the roller for rotation therewith. The roller is movable toward one of sheets advancing in juxtaposed relation in a common plane, so that it is brought into engagement with the advancing sheet to be driven for rotation and displaces it out of the common plane to expose the lateral edge of the adjoining sheet. One end of the coloring element is brought into contact with the exposed lateral edge of the adjoining sheet to provide a colored marking thereto. As shown in FIG. 1A, the coloring element C is disposed in such a manner as to slightly overlap the sheet S an amount O. If the amount O is excessive, the end of the coloring element C is brought into contact not with the lateral edge of the sheet S but with the marginal portion of the sheet S, as best shown in FIG. 1B. This will affect the quality of the final sheet. In addition, when the marking operation is carried out in this condition, the peripheral surface of the coloring element C adjacent to the end face thereof is worn as shown in FIGS. 1C and 1D to aggravate the